The present invention is generally directed to non-invasive medical procedures for measuring a person's (or animal's) blood-related signals, and more particularly to a method and pulse oximeter apparatus for measuring blood-oxygen levels that uses chemical heating.
Pulse oximetry is a procedure used to monitor blood arterial oxygen saturation (SaO2) levels and pulse rates noninvasively. Pulse oximetry is used in operating rooms, ICU, during emergency transport, etc.
Currently, there are two modes of pulse oximetry sensor configurations: the transmission mode and the reflectance mode. The transmission mode often is used when a pulse oximeter probe is placed on the finger, ear lobe or toe. This mode uses an optical emitter and a detector positioned on opposite sides of the tissue through which the measurement is to be made. The reflectance mode often is used on the forehead and the optical emitter and the detector are positioned side by side. In both types, the pulse oximeter probes transmit red and infrared light through blood-perfused tissue, for example, the arterial vascular bed. The detector measures the transmitted light as it passes through the vascular bed, thereby detecting the amount of colored light absorbed by the arterial blood, and from this the arterial oxygen saturation level is calculated.
While pulse oximetry has become a standard for measuring oxygen saturation, there are number of situations where it performs poorly. For example, variations in the tissue temperature in the region of the measurement site can affect the accuracy of the measurements by affecting blood perfusion. Low tissue temperatures result in vascoconstriction and low blood perfusion, which make it difficult to obtain valid SaO2 pulse rate values. The inability to obtain accurate SaO2 and pulse readings can lead to misdiagnosis, incorrect treatment, or procedures to be canceled. SaO2 and pulse readings are important to maintain patient stability during diagnostic testing, surgical procedures and monitoring, while in critical care areas. Changes in SaO2 and pulse rate are important to monitor in order to be able to compensate for any decrease in patient oxygen saturations during hemodynamic monitoring.
Various methods have been tried over the years for increasing the measurement site tissue temperature in conjunction with pulse oximetry measurements. Some of these methods are described in the following patent documents: U.S. Pat. No. 4,926,867 to Kanda et al., U.S. Pat. No. 5,131,391 to Sakai et al., U.S. Pat. No. 6,343,223 B1 to Chin et al., U.S. Pat. No. 6,466,808 B1 to Chin et al., U.S. Pat. No. 6,839,579 B1 to Chin; U.S. Patent Application Publication Nos. 2003/0040783 A1 to Salmon, 2005/0101851 A1 to Chin, 2005/0209516 A1 to Fraden; European Patent No. EP 1 538969 B1 to Welsch Allyn, Inc.; and PCT International Pub. No. WO 2009/032074 A 1 to Woolsthorpe, LLC (the '074 application). In most of these methods, the heat is applied by the use of an electrical heating source.
However, the '074 application goes further and describes the use of any “heating means”, which it defines as including “any means of increasing the core or tissue temperature of a subject, including, without limitation, one or more (i.e., in combination of) devices that transmit heat energy, such as thermoelectric heating devices (e.g., heating elements of various sizes, shapes, materials, etc. that are adapted to cooperate with various heating apparatus and/or configurations, such as a heated glove), contact heaters, lamps, heating blankets, etc., heated rooms, heated liquids, devices that transmit ultrasonic or photoelectric energy, and mentholated, counterirritant and/or vasodilating substances . . . [and] also means includes passive heating means, i.e., means for limiting heat from escaping a specific tissue region of the body.” The '074 application emphasizes the application of heat over a large tissue region, such as an entire organ, appendage, or the entire body, but also notes that the heat can be applied to smaller regions, e.g., a single finger in conjunction with obtaining a pulse oximeter reading on the finger. It also teaches the optional use of sensors to monitor the skin temperature during heating.
Various other sensors/monitors are disclosed in U.S. Pat. No. 6,385,821 to Modgil et al, U.S. Pat. No. 6,731,963 to Finarov et al., U.S. Pat. No. 7,650,177 to Hoarau et al., U.S. Pat. No. 7,869,850 to Hoarau et al., and PCT International Pub. No. WO 2005/010568.
Nonetheless, an improved pulse oximeter probe can be envisioned which includes self-contained non-electric heating means.